Because of the way Eventlet, which Spawning depends on, installs itself, it can't be installed into a virtualenv. The following error (wrapped for readability) illustrates:
Running eventlet-0.9.4/setup.py -q bdist_egg --dist-dir \
/tmp/easy_install-m_s75o/eventlet-0.9.4/egg-dist-tmp-fAZK_u
error: SandboxViolation: chmod('/home/myuser/.python-eggs/\
greenlet-0.2-py2.6-linux-i686.egg-tmp/tmpgxa_uc.$extract', 493) {}
Without patching the Python path beyond all recognition, and installing Spawning globally (which would break the whole point of having a virtualenv anyway), how would one install/run this?